1. Field of the Invention
The present invention relates to battery packs, and particularly, to a battery pack which is provided with a protection sheet disposed between a secondary battery and a control circuit-board, and which achieves a compact structure without sacrificing the ability to prevent an electrolyte from adhering to the control circuit-board.
2. Description of the Related Art
A typical battery pack is installed in a main-body unit of an electronic apparatus, such as a personal computer, and drives the battery for the main-body unit.
Battery packs are generally provided with a casing in which a single secondary battery or a plurality of secondary batteries is disposed. Moreover, the casing also contains a control circuit-board for charging and discharging the secondary battery or secondary batteries. Lithium-ion batteries are widely used for the secondary batteries, and combustible organic solvents are generally used for the electrolyte contained in the battery cells.
If such secondary batteries are used in an environment where the temperature and the pressure are high, for example, there may be cases where the electrolyte leaks or evaporates from the interior of the battery cell depending on the contact between the positive terminal and the battery cylinder, i.e. the outer casing of the battery cell. This may be problematic if the electrolyte leaks or evaporates and thus adheres to the control circuit-board. This could lead to problems, such as a short circuit in the control circuit-board, dysfunction of electronic components on the control circuit board, or an insulation failure caused by a migration of a metallic material to an insulative material.
To solve such problems caused by the leakage or evaporation of an electrolyte, Japanese Unexamined Patent Application Publication No. 8-293327 discloses a battery pack including a casing in which a barrier wall is provided for separating the secondary batteries from the control circuit-board. Such a structure prevents the electrolyte from entering the control circuit-board.
According to such a conventional battery pack, however, the barrier wall inside the casing generally requires a thickness of about 1 mm for, for example, rigidity. For this reason, a predetermined space must be provided for the barrier wall. This is problematic in that it is difficult to make the battery pack sufficiently compact.
Furthermore, since the barrier wall is integrally disposed in the casing in most cases, if the thickness of the barrier wall is reduced to achieve a compact structure for the battery pack, the fluidity of the molding resin used for fabricating the casing becomes deteriorated. This may lead to higher manufacture costs for the battery pack since exact values may be required for the molding conditions, such as the molding temperature and injection speed.
Furthermore, since such a structure is complex due to having the barrier wall inside the casing, such a structure can lead to molding errors caused by, for example, weld marks and sink marks.
Moreover, if the battery pack receives an external impact due to, for example, dropping or vibration of the battery pack, the impact may transmit to the barrier wall and can thus cause the barrier wall to crack or break. This is problematic in that the electrolyte may enter the control circuit-board. Such a problem of the electrolyte entering the control circuit-board due to the cracking or breakage of the barrier wall is likely to occur especially in cases where the barrier wall is integrally disposed in the casing since the impact can easily transmit to the barrier wall.